曝光台 注意防骗
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Spacecam is a gyro-stabilised affair
that lives in a large round casing on
the front of an AStar:
(OK, so it's a Twinstar – it fits both)
The electronics are so good that you
can take a fair amount of turbulence
without the camera even seeing it.
The flying itself includes a little
formation work here and there,
some precision hovering, or crosscontrolling
when you have to make
sharp, level turns. You need to be
smooth on the controls, operate
safely and ensure there is plenty of
communication, but most important
is knowing the performance limits of
your machine.
Directions, when given, are in
relation to the camera, as in "Camera
Right" or "Camera Left". Otherwise,
if you don't have an aviation liaison
person, you can expect all kinds.
Aerial Survey
This is the process of photographing
areas of land from varying heights,
the results generally used for mapmaking.
As a result, this takes place
at great heights, but it may get
exciting and bring you down to 300
feet, depending on the results
required. Aerial survey can give good
job satisfaction, especially when you
can see the results, and the target
appears in every frame as requested
by the surveyor.
When doing low-level work, you will
be given a large-scale map with flight
patterns marked on it, and you do
everything by pure map reading. The
pattern can be star-shaped, with sets
of two or three parallel runs at angles
to each other over the target. The
equipment used is something like the
Zeiss trilens, which will take one flat
and two oblique photographs at the
same time. You can work at higher
levels with a 35mm, but you will
need a navigation aid, like Decca
Navigator, or GPS, as close mapreading
is not so easy up there.
With 35mm at least, as the focal
length decreases, depth perception
increases, and required altitude
decreases. Your camera can either be
aligned transversely (i.e. in landscape
mode), or longitudinally; the former
makes for easier navigation, and
should be used for overlapping
strips, but the latter is more flexible.
As to results, a 28-times enlargement
is used for display purposes,
otherwise a contact strip with a 7x
stereoscope is good enough for most
work except map revision, which
needs to be blown up around 6.3
times. A larger scale makes the
results easier to read, but you need
to fly lower and take more photos.
You need to know such things to
use certain tables that give you
altitudes to fly to get proper
coverage, from 500 to 11000 feet,
that is, the lowest for low flying and
the highest without oxygen. They
also give you the speeds to be flown
and the intervals between pictures,
which will ultimately tell you how
long you will be flying and how
much to charge the customer. The
Specialised Tasks 85
book with all these in is called
Parameters and Intervals for 35mm Aerial
Photography.
Normally use a shutter speed of
1/500th of a second, or 1/250th if the
light is bad. Make sure the camera is
set to the ASA rating of the film.
Use a 28 mm lens above 4000’ and
35 mm for lower, and focus to
infinity. A yellow filter is needed for
winter B/W photography.
Air Testing
If you're a junior pilot, you may find
yourself doing quite a bit of this,
anything from just engine running to
full C of A air tests, although many
engineers are cleared for engine runs.
The reason why junior pilots tend do
them is because they're boring and
regarded as a waste of time by
anyone except engineers.
Nevertheless, Air Testing demands
your full concentration and everyone
due to fly in the aircraft later
deserves it as well. One point to bear
in mind is that the aircraft is only
technically serviceable for the air
test—if in doubt, insist that an
engineer goes with you; if he won't
fly, then don't you bother either.
The least taxing are straight engine
runs. When a sliver of metal is
detected in oil, there can follow an
engine run for anything up to two
hours or so (I have known one for
five) to see if it happens again. Then
there are compass swings where you
place the aircraft on a series of
headings on an isolated spot well
away from large hangars and other
machines, while someone with a
landing compass stands outside in
the cold and rain taking readings.
Comparison of your readings with
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The Helicopter Pilot’s Handbook(57)
